What Is The Delta

River delta ecosystem

About 2500 years ago, the Greek historian Herodotus noticed that the mouth of the Nile river formed a triangular shape that resembled the Greek letter “delta.” It is from this that a delta–the landform created at the point where a river flows into the ocean, sea or lake–gets its name.


River delta ecosystem

When the flowing water of a river hits the standing water of an ocean, lake or reservoir, the river water overflows its channel and expands in width. The wider water pathway slows the speed of the river water. This drop in speed allows the sediments that are carried by the river to accumulate at the point where the river meets the standing body of water. The mouth of the river will also expand by breaking up into multiple channels, with the land between the channels consisting of swamp or marshy areas.

Types of Deltas

Deltas are often categorized based whether sediment deposition was created by rivers, waves or tides. These differences affect the shape of the delta. River-dominated deltas frequently take the shape of a bird’s foot, since its main channel branches off into many smaller channels. This occurs when the slope of the river channel is lower than other available courses. The water breaks off from the main channel and forges, new quicker routes to the ocean. Wave erosion creates wave-dominated deltas which take the classic triangular shape. Deltas created by tide erosion tend to take a “dentritic” shape.

Famous Deltas

River deltas have attracted human settlements for centuries. Rich soil and close proximity to fresh water allowed early communities near the Nile and the Tigris-Euphrates deltas to thrive. The Ganges river in India culminates in world’s largest delta. The delta of the Volga, which cuts through western Russia, is Europe’s largest, while the Danube delta is Europe’s best preserved. The Mississippi delta, which empties into the Gulf of Mexico, served as the setting for several novels by southern author William Faulkner.

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Ecological Threats

Human interference is often detrimental to sensitive delta ecosystems. Dams and reservoirs built to generate hydroelectric power restrict the flow of fresh water to the delta and cause it to erode. For example, when the Hoover Dam was erected in 1930 on the Colorado River, the delta wetlands, deprived of a steady stream of fresh water dwindled to about five percent of its original area. With a weakened ecosystem, invasive, non-native plants over-took indigenous ones to further devastate the area. Heavy flooding in the 1980s and 1990s, however, helped to reinvigorate the delta.

Deltas on Mars

In July of 2008, NASA released findings gathered from their Mars Reconnaissance Orbiter, which indicated the presence of large, numerous bodies of water on the Red Planet. These wetlands, scientists speculate, could have supported life. Scientist Bethany Ehlmann, who composed a study on an ancient lake in the northern Martian region called “Jezero Crater” stated that the clay sediments in the delta that empties into the ancient lake are “wonderful at trapping and preserving organic matter, so if life ever existed in this region, there’s a chance of its chemistry being preserved in the delta.”